I'm Lawrence from the Asana Product team! Thanks so much for posting on the community - we love hearing about how you're using the product and your product feedback.
Just to add on to Alexis' advice, two other suggestions I may add. First, the Completed Tasks view is, by default, sorted by descending Completion Date (i.e. most recent tasks at the top), so you should be able to get a sense of recently completed work just by looking at what's at the top of the list.
Second, there's also the ability to do (and star) an Advanced Search limited to Completed Tasks within a time range. To do this:
1. Go to the Search bar > Advanced Search
2. Under "In Projects", enter in your scrum project's name
3. Under "Completion", set it to "Completed"
4. Under "Add Filter", add a Completion Date and indicate how many days / weeks back you'd like to see completed tasks for.
Hope this helps.
A question I have for you - I'd love to know a bit more about your use case for the Tasks Completed recently views. You mentioned you were using it for your scrum projects. Can you tell me a little bit more about how you use these views in your scrum? When in the scrum process did you use the views, what did the team use them for, how did it factor into any of your analysis or scrum processes, etc.?